Drying Hardwood Lumber using Radio Frequency

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Ursula Peters
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1 Drying Hardwood Lumber using Radio Frequency Workshop Regional Hardwood Initiative September 21, 2010 Forestry Center, Fredericton Vincent Lavoie, Researcher in wood drying (FPInnovations) James Kendall, Researcher (LTE)

Forestry Center, Fredericton Vincent Lavoie,

2 Presentation outline RF drying basic principles and justification for hardwood drying Summary of RFV drying work that has been performed by FPInnovations and Hydro-Quebec between 2001 and 2008 RF continuous drying idea RF continuous drying tests on hardwoods Technical and economical analysis to develop potential applications in hardwood sector RF continuous tests on low grade hardwoods Conclusion

continuous drying idea RF continuous drying tests on hardwoods Technical and economical analysis to

3 RF drying basic principles and justification for hardwood drying Water molecules (+ : H, - :O) Ref: RF is a volumetric heating in the material versus convective and conductive ways that heat from the outside = less shrinkage variation = less constraint = drying speed can be increase = interresting for thick pieces No stickers needed

com RF is a volumetric heating in the material versus convective and conductive ways that

4 Work performed with RFV lab kiln Principal conclusions with hardwoods Excellent drying time for many products/species Product 12/4 red oak 4/4 hard maple 8/4 hard maple DT (days) RFV 4 to DT (days) Conventionnal 150 to

products/species Product 12/4 red oak 4/4 hard maple 8/4 hard

5 Work performed Principal conclusions with hardwoods Low MC gradients in thickness Low residual stress Natural color conserved Low degrade Final MC variation (between pieces) too important for hardwood products Presorting/redrying strategies could help to improve final MC distribution

degrade Final MC variation (between pieces) too important for hardwood

6 Work (objectives) Continue to explore/identify drying potential applications for RFV technology Study redrying approach Develop technics/strategies to improve products quality (warpage, final MC distribution)

7 Explore/identify drying potential applications Conclusion, the best application for that technology Thick pieces with not too small final MC variation

8 Re-drying approach study using RFV Good conclusions and good payback for RFV redrying but: Better payback with conventional kilns Rehandling and management costs block the technics implementation

9 Solution, RF continuous redrying system at the planer mill System advantages: Automatic pieces handling without piling Energy consumption lower than RFV technology Better final MC control (piece by piece) ROI possibly shorter than with RFV technology

Energy consumption lower than RFV technology Better final MC

10 Continuous RF VS conventionnal redrying NO WEIGHT Weight (3000 pounds)

11 Red oak 12/4 trial Presentation of results Hardwood TAC spring 08

12 Preliminary results for red oak 12/ Teneur Moisture en humidité content (%) (%) Pieces Final MC (%) Pass number Numéro de la passe AVG (%) 7.1 Pièce #1 Pièce #3 Pièce #4 Pièce #5 Pièce #6 Pièce #7 Pièce #8 STD (%) 1.2 % Pces±2% Avg MC. 86

33 31 29 27 25 23 21 19 17 15 13 11 9 7 5 3 1 3 7.6 Pieces Final MC (%) 4 7.0 5 5.9 6 6.5 7.

13 Preliminary results for red oak 12/ Coeur Intermédiaire Surface TH moyenne 23 Teneur Moisture en humidité content (%) Piece Numéro number de pièce

Moisture en humidité content (%) 21 19 17 15 13

14 Preliminary results for red oak 12/4

15 Drying trial on Hard Maple 4/4, color impact Results presentation, Hardwood TAC Winter 09

16 Results trial no.3 (color) Piece # (Beech) E* ab green vs dry If E* ab value < 3, change in color cannot be seen by the human eye Conclusion: The technology has no impact on color Green T=0 Hours Dry T=2.4 Hours

17 Results trial no.3 (drying time) 50% 45% 40% Beech piece Moisture Teneur en content humidité 35% 30% 25% 20% 15% 10% 5% 2.4 HOURS! 0% 0,0 0,5 1,0 1,5 2,0 2,5 3,0 Temps Drying de séchage Time (hours) (heures) Pièce 11 Pièce 12 Pièce 13 Pièce 14 Pièce 15

18 Meeting of 6 industrials to discuss the potential of this thechnology Energy cost to dry by RF Application Séchage complet/re-séchage par HF (Teneur finale = 8%) Energy cost for differents initial MC to a final MC of 8% 70 $ 60 $ Energy cost ($/Mbf) Coût séchage HF ($/Mpmp) 50 $ 40 $ 30 $ 20 $ Re-drying Re-séchage? 0,04 $ 0,06 $ 0,08 $ 10 $ 0 $ Thi (%) Initial MC (%)

initial MC to a final MC of 8% 70 $ 60 $ Energy cost ($/Mbf) Coût séchage HF ($/Mpmp) 50 $ 40 $

19 Meeting of 6 industrials to discuss the potential of this thechnology Equipment cost and electrode lenght (total) for: DRYING APPLICATION FROM 60 TO 8% MC Coût d'équipement vs productivité et temps d'opération quotidien (60% à 8%) Equipement cost Longueur d'électrodes vs productivité et temps d'opération quotidient (60%à 8%) Electrode lenght Cost Coût (M$) heures 18 heures 24 heures Electrode Longueur lenght électrodes (meters) (m) heures 18 heures 24 heures Annual Productivité production (MMpm(MMbf) p) Annual Productivité production (MMpm(MMbf) p)

8%) Electrode lenght Cost Coût (M$) 20 18 16 14 12 10 8 6 4 2 0 0 10 20 30 12 heures 18 heures 24 heures Electrode Longueur lenght électrodes (meters) (m) 1000 900

20 Meeting of 6 industrials to discuss the potential of this thechnology Equipment cost and electrode lenght for: PRE-DRYING APPLICATION FROM 60 TO 30% MC Coût d'équipement vs productivité et temps d'opération quotidien (60% à 30%) Equipement cost Longueur d'électrodes vs productivité et temps d'opération quotidient (60%à 30%) Electrode lenght Cost Coût (M$) heures 18 heures 24 heures Electrode Longueur lenght électrodes (meters) (m) heures 18 heures 24 heures Annual Productivité production (MMpm (MMbf) p) Annual Productivité production (MMpm (MMbf) p)

30%) Electrode lenght Cost Coût (M$) 20 18 16 14 12 10 8 6 4 2 0 0 10 20 30 12 heures 18 heures 24 heures Electrode Longueur lenght électrodes (meters) (m) 1000

21 Meeting of 6 industrials to discuss the potential of this thechnology Equipment cost and electrode lenght for: RE-DRYING APPLICATION FROM 15 TO 8% MC Coût d'équipement vs productivité et temps d'opération quotidien (15% à 8%) Equipement cost Longueur d'électrodes vs productivité et temps d'opération quotidient (15%à 8%) Electrode lenght Cost Coût (M$) heures 18 heures 24 heures Electrode Longueur lenght électrodes (meters) (m) heures 18 heures 24 heures Annual Productivité production (MMpm (MMbf) p) Annual Productivité production (MMpm (MMbf) p)

22 Conclusions of industrial meetings For a 10 MMbf/year capacity hardwood mill operating 18 hours/day The technology cost is estimated to: 5 Millions $ for drying green to dry (60%-8%) 3 Millions $ for pre-drying (60%-30%) 1.5 Millions $ for re-drying (15%-8%) The energy cost is estimated to: 50$/Mbf for drying green to dry 33$/Mbf for pre-drying 12$/Mbf for re-drying

23 Conclusions of industrial meetings Even if industrials were surprised by the potential price of equipment, 5 on 6 want that we continue to work on development of this technology for hardwood applications Interest for green to dry application Determine if there s a value added related to the technology, specially for low grade products Interest for pre-drying Determine what is the value added related to that practice Determine what is the maximum MC acceptable to stop stain development Interest for re-drying Determine final quality of the product

24 Trial to determine if there is a value added using continuous RF drying technology to dry low grade hardwoods 20 twin boards dried by two technologies (continuous RF and conventionnal) 10 Initial grading Fréquence (nombre de pièces) HF CONV 1 0 2S 3S 2 3 3B Grade

25 Trial to determine if there is a value added using continuous RF drying technology to dry low grade hardwoods Operation parameters Conventionnal RF continuous Heat up Dry bulb temp. ( o F) 100 Wet bulb temp. ( o F) 92 Duration (hours) 4 Power density: from 86 to 238 kw/m³ Step Tension: 2.2 à 2.7 kv Step 2 Step Conveyor speed: 6 in/minute Step Step Step Step Step

26 Trial to determine if there is a value added using continuous RF drying technology to dry low grade hardwoods Results MC i (STD) MC f (STD) Drying time (hours) Value before drying ($/Mbf) Value after drying ($/Mbf) Degrade (value loss) HF continu 56.4% 8.2% 3 à $/Mpmp (7.3%) (0.8%) Conventionnel 57.7% 7.5% $/Mpmp (7.9%) (0.5%) Value lost for dimension (shrinkage): 2 pieces for RF, 1 piece conventional

27 Trial to determine if there is a value added using continuous RF drying technology to dry low grade hardwoods Problem that occurs during the tests with low grade material dried by continuous RF technology Electrical arc in heartwood and decay wood that burns the wood

28 Conclusions on hardwoods RF continuous drying past performed works The main obstacle to implementing RFV technology in hardwood sector is the too large MC variation between pieces after drying Drying by continuous RF can address the final MC variation problem because the moisture content is controlled piece by piece Drying by continuous RF does not change de color of light woods as Sugar Maple The first drying test with RF continuous technology on Sugar Maple has been realised in 2.4 hours

29 Conclusions sur les travaux réalisés jusqu ici sur le séchage des bois feuillus par HF Continuous RF drying of maple low grade material from green to dry does not add value to the product The two main applications that need to be studied in future work with hardwoods are: Pre-drying of high grade material (to prevent stain on green wood) Fast redrying of pre-dried material to give better flexibility and agility to the global tranformation process

KILN SCHEDULES HARDWOOD KILN SCHEDULES KILN SCHEDULES KILN SCHEDULES KILN SCHEDULES KILN SCHEDULES

KILN SCHEDULES HARDWOOD KILN SCHEDULES KILN SCHEDULES KILN SCHEDULES KILN SCHEDULES KILN SCHEDULES HARDWOOD with emphasis on oak NINE DRYING PRINCIPLES pp. 72-72 in DRYING HARDWOOD LUMBER 1. MC Basis Wettest half (many use the wettest) 10-12 samples 2. MC is Average (not shell or core) 3. Visual inspection